The present invention concerns a video system for assisting automobile traffic wherein traffic flow and traffic build-up signals are transmitted along a radio-frequency channel by a transmitter unit to receiver units placed in motor vehicles and are displayed on screens that can be seen by the drivers.
The transmitter unit transmits a series of images or messages in sequence concerning only traffice flow and build-up indications to the exclusion of plans or maps of the zones to which the indications refer. These plans or maps are memorized in the receiver unit and can be selected and displayed on the display screen. The indication signals contain the information required for identifying the map or plan to which they refer and for localizing them on this plan or map.
It thus results that the complete map or plan of traffic flow and build-up in a sector comprises a map or plan background memorized locally and displayed as an image fixed part and a traffic flow and build-up indication superimposed on the screen on this map or plan background which constitutes a variable part of the image. The image or the message transmitted by the transmitter unit contains only this variable information to the exclusion of any basic fixed information.
This image or message therefore only calls for a small pass band and the transmission is made at a relatively low carrier frequency of the same magnitude as those used for communications between fixed and moving units and not at a UHF carrier frequency approaching those used in television networks.